Power management circuit and a method for operating a power management circuit

ABSTRACT

A power management circuit and a method for operating a power management circuit are described. In one embodiment, a power management circuit includes power switching modules. Power is supplied to each of the power switching modules by at least one of multiple power sources. Each of the power switching modules includes a latch circuit configured to have a definite state at power-up of a corresponding power source and a logic circuit configured to control power supplied from the corresponding power source in response to the definite state of the latch circuit, where the logic circuit includes a cross-coupled circuit. Other embodiments are also described.

Embodiments of the invention relate generally to electronic hardware andmethods for operating electronic hardware, and, more particularly, topower management circuits and methods for operating power managementcircuits.

Some electronic devices are powered by multiple power sources. Forexample, a radio frequency identification (RFID) device may be poweredwirelessly by an RF electromagnetic field and by a local power sourcesuch as a battery. Power management circuits are used to manageelectronic devices that support multiple power sources. For example, apower management circuit is used to control power supplied to anelectronic device based on the availability of power sources and tohandle the transition between the power sources.

Conventional power management circuits for devices that support multiplepower sources suffer from various drawbacks. For example, a conventionalpower management circuit typically cannot ensure a smooth transition ofpower from one power source to another power source without interruptingthe power supplied to an onboard integrated circuit (IC) device. Inaddition, a conventional power management circuit can cause crossconduction between different power sources. Consequently, a conventionalIC device that supports multiple power sources can have startup issues,which may cause a failure of the IC device. Therefore, there is a needfor a power management circuit for multiple power sources that allows asmooth transition between different power sources and reduces crossconduction between the different power sources.

A power management circuit and a method for operating a power managementcircuit are described. In one embodiment, a power management circuitincludes power switching modules. Power is supplied to each of the powerswitching modules by at least one of multiple power sources. Each of thepower switching modules includes a latch circuit configured to have adefinite state at power-up of a corresponding power source and a logiccircuit configured to control power supplied from the correspondingpower source in response to the definite state of the latch circuit,where the logic circuit includes a cross-coupled circuit. The latchcircuit differs from a conventional latch at power-up in the sense thatthe power supply terminal itself acts as the input to the latch circuitand enables the latch circuit to be configured in a defined outputstate. Using a latch circuit having a definite state at the power-up ofpower source and a logic circuit with a cross-coupled circuit, the powermanagement circuit is able to smoothly transition between differentpower sources and reduce cross conduction between the different powersources. Other embodiments are also described.

In an embodiment, a power management circuit includes power switchingmodules. Power is supplied to each of the power switching modules by atleast one of multiple power sources. Each of the power switching modulesincludes a latch circuit configured to have a definite state at power-upof a corresponding power source and a logic circuit configured tocontrol power supplied from the corresponding power source in responseto the definite state of the latch circuit, where the logic circuitincludes a cross-coupled circuit.

In an embodiment, a power management circuit includes a first powerswitching module and a second power switching module. Power is suppliedto the first power switching module by a wireless power source. Power issupplied to the second power switching module by a battery power source.Each of the first and second power switching modules includes aback-to-back inverter latch circuit configured to have a definite stateat power-up of a corresponding power source and a logic circuitconfigured to control power supplied from the corresponding power sourcein response to the definite state of the back-to-back inverter latchcircuit. The logic circuit includes a cross-coupled circuit and a switchcircuit connected to the corresponding power source.

In an embodiment, a method for operating a power management circuitinvolves providing power switching modules, where power is supplied toeach of the power switching modules by at least one of multiple powersources, operating a latch circuit of each of the power switchingmodules to have a definite state at power-up of a corresponding powersource, preventing cross conduction between the power sources using alogic circuit of each of the power switching modules, and connecting oneof the power sources to an output of the power management circuit basedon the definite states of the latch circuits.

Other aspects and advantages of embodiments of the present inventionwill become apparent from the following detailed description, taken inconjunction with the accompanying drawings, depicted by way of exampleof the principles of the invention.

FIG. 1 is a schematic block diagram of an IC device in accordance withan embodiment of the invention.

FIG. 2 depicts an embodiment of the power management circuit depicted inFIG. 1 that is used with a wireless power source and a battery powersource.

FIG. 3A depicts an embodiment of one of the latch circuits depicted inFIG. 2.

FIG. 3B depicts a switching point threshold diagram of the latch circuitdepicted in FIG. 3A.

FIG. 4 depicts a signal diagram of the power management circuit depictedin FIG. 2 in a power-up sequence where the wireless power source ispresent and the battery power source is absent.

FIG. 5 depicts a signal diagram of the power management circuit depictedin FIG. 2 in a power-up sequence where the battery power source ispresent and the wireless power source is absent.

FIG. 6 depicts a signal diagram of the power management circuit depictedin FIG. 2 in a power-up sequence where the wireless power source ispresent first and the battery power source is present later.

FIG. 7 depicts a signal diagram of the power management circuit depictedin FIG. 2 in a power-up sequence where the battery power source ispresent first and the wireless power source is present later.

FIG. 8 depicts a signal diagram of the power management circuit depictedin FIG. 2 in a power-up sequence where the battery power source and thewireless power source are present simultaneously.

FIG. 9 depicts another embodiment of the power management circuitdepicted in FIG. 1 that is used with a wireless power source and abattery power source.

FIG. 10 is a process flow diagram of a method for operating a powermanagement circuit in accordance with an embodiment of the invention.

Throughout the description, similar reference numbers may be used toidentify similar elements.

It will be readily understood that the components of the embodiments asgenerally described herein and illustrated in the appended figures couldbe arranged and designed in a wide variety of different configurations.Thus, the following detailed description of various embodiments, asrepresented in the figures, is not intended to limit the scope of thepresent disclosure, but is merely representative of various embodiments.While the various aspects of the embodiments are presented in drawings,the drawings are not necessarily drawn to scale unless specificallyindicated.

The described embodiments are to be considered in all respects only asillustrative and not restrictive. The scope of the invention is,therefore, indicated by the appended claims rather than by this detaileddescription. All changes which come within the meaning and range ofequivalency of the claims are to be embraced within their scope.

Reference throughout this specification to features, advantages, orsimilar language does not imply that all of the features and advantagesthat may be realized with the present invention should be or are in anysingle embodiment. Rather, language referring to the features andadvantages is understood to mean that a specific feature, advantage, orcharacteristic described in connection with an embodiment is included inat least one embodiment. Thus, discussions of the features andadvantages, and similar language, throughout this specification may, butdo not necessarily, refer to the same embodiment.

Furthermore, the described features, advantages, and characteristics ofthe invention may be combined in any suitable manner in one or moreembodiments. One skilled in the relevant art will recognize, in light ofthe description herein, that the invention can be practiced without oneor more of the specific features or advantages of a particularembodiment. In other instances, additional features and advantages maybe recognized in certain embodiments that may not be present in allembodiments of the invention.

Reference throughout this specification to “one embodiment,” “anembodiment,” or similar language means that a particular feature,structure, or characteristic described in connection with the indicatedembodiment is included in at least one embodiment. Thus, the phrases “inone embodiment,” “in an embodiment,” and similar language throughoutthis specification may, but do not necessarily, all refer to the sameembodiment.

FIG. 1 is a schematic block diagram of an IC device 100 in accordancewith an embodiment of the invention. The IC device can be used invarious applications, such as communications applications, industrialapplications, medical applications, computer applications, automotiveapplications, and/or consumer or appliance applications. The IC devicecan be implemented in a substrate, such as a semiconductor wafer or aprinted circuit board (PCB). In an embodiment, the IC device is packagedas a semiconductor IC chip. In some embodiments, the IC device isincluded in a computing device, such as a smartphone, a tablet computer,a laptop, etc. The IC device may be an RFID device that is poweredwirelessly by RF electromagnetic signals and by a local power sourcesuch as a battery. For example, the IC device may be included in a NearField Communications (NFC) capable computing device.

In the embodiment depicted in FIG. 1, the IC device 100 includes powersources/supplies 102-1, . . . , 102-N, where N is an integer that islarger than 1, and a power management circuit 104. The power sources102-1, . . . , 102-N of the IC device may include any type of powersupplies. In some embodiments, the power sources include at least onecontactless power source. For example, the power management circuit mayinclude an inducer that can be charged wirelessly by electromagneticsignals. In some embodiments, the power sources include at least onebattery power source. For example, the power sources may include alithium battery and/or any other type of battery.

The power management circuit 104 is configured to manage the powersources 102-1, . . . , 102-N. In an embodiment, the power managementcircuit is configured to control power supplied to the IC device basedon the availability of the power sources and to handle the transitionbetween the power sources based on predefined precedence. In theembodiment depicted in FIG. 1, the power management circuit includes anumber of power switching modules 106-1, . . . , 106-N. Each of thepower switching modules is supplied by a corresponding one of the powersources. Each of the power switching modules includes a latch circuit108-1, . . . , or 108-N configured to have a definite state at power-upof a corresponding power source and a logic circuit 110-1, . . . , or110-N configured to control power supplied from the corresponding powersource in response to the definite state of the latch circuit. In anembodiment, the logic circuit is configured to connect the correspondingpower source to an output terminal 112 of the power management circuitor to disconnect the corresponding power source from the output terminalof the power management circuit based on the state of the latch circuit.Using the latch circuit having a definite state at the power-up of powersource and the logic circuit with the cross-coupled circuit, the powermanagement circuit allows for smooth transition between different powersources and reduces cross conduction between different power sources.

Although the IC device 100 is depicted and described with certaincomponents and functionality, other embodiments of the IC device mayinclude fewer or more components to implement less or morefunctionality. For example, the IC device may include one or more powerinterfaces between the power sources and the power management circuit.In some embodiment, one or more power sources is not part of (e.g.,external to) the IC device. In an embodiment, the IC device includes alocal power source (e.g., a battery power source) and the powermanagement circuit 104. In this embodiment, a remote power source (e.g.,a contactless/wireless power source) is not included in the IC device.

In some embodiments, the power management circuit 104 is used with awireless power source and a battery power source. FIGS. 2 and 9 depicttwo embodiments of the power management circuit depicted in FIG. 1 thatare used with a wireless RF electromagnetic power source and a batterypower source.

FIG. 2 depicts a first embodiment of the power management circuit 104depicted in FIG. 1 that is used with a wireless RF electromagnetic powersource 202-1 and a battery power source 202-2. In the embodimentdepicted in FIG. 2, a power management circuit 204 includes two powerswitching modules 206-1, 206-2. The power switching module 206-1 issupplied by the wireless power source with a voltage, “V_(RF).” In someembodiments, the power management circuit includes an inducer that canbe charged wirelessly by electromagnetic signals from the wireless powersource. The power switching module 206-2 is supplied by the batterypower source with a voltage, “V_(CC)”.

The power switching module 206-1 includes a latch circuit, “L1,”configured to have a definite state at power-up of the wireless powersource 202-1 and a logic circuit 210-1 configured to prevent crossconduction between the wireless power source and the battery powersource 202-2 and to connect/disconnect the wireless power source to/froman output terminal 212 of the power management circuit 204. In theembodiment depicted in FIG. 2, the latch circuit, “L1,” is a back toback inverter latch circuit that includes two inverters, “INVL11,”“INVL12,” which are connected back to back. The back to back inverterlatch circuit has a dynamic switching point threshold that scales wellwith the voltage level, “V_(RF),” of the wireless power source andallows the back to back inverter to have a defined state at power-up ofthe wireless power source with a good noise margin. In some embodiments,the latch circuit is overridden by a driver circuit (e.g., an AND gate,“A1”) to flip the state based on a power-up preference setting tooverride the logic when multiple power sources are available. The drivercircuit may be applied only to the power switching module that does nothave the precedence. In the embodiment depicted in FIG. 2, the Vrf doesnot have the precedence. The logic circuit includes a cross-coupledcircuit 211-1, which includes four transistors, “M1,” “M2,” “M3,” “M4,”a power switch that is implemented as a p-channelmetal-oxide-semiconductor field effect transistor (PMOS) transistor,“M13,” AND gates, “A1,” “A2,” a buffer circuit, “B1,” transistors, “M9,”“M10,” and a resistor, “R1.” A node, “N1,” between the PMOS transistor,“M1,” and the NMOS transistor, “M2,” is connected to a terminal 214(e.g., a drain terminal or a source terminal) of the PMOS transistor,“M3.” A node, “N2,” between the PMOS transistor, “M3,” and the NMOStransistor, “M4,” is connected to a terminal 216 (e.g., a drain terminalor a source terminal) of the NMOS transistor, “M2.” Gate terminals 218,220 of the PMOS transistor, “M1,” and the NMOS transistor, “M2,” areconnected to a terminal, “a,” of the latch circuit, “L1.” Gate terminals222, 224 of the PMOS transistor, “M3,” and the NMOS transistor, “M4,”are connected to a terminal, “d,” of a latch circuit, “L2,” of the powerswitching module 206-2. The cross-coupled circuit 211-1 allows a breakbefore a make operation to inhibit or prevent a current path between theRF electromagnetic voltage, “V_(RF),” and the battery voltage, “V_(CC)”In an embodiment, the cross-coupled circuit 211-1 ensures that theswitch, “M14,” is switched off before the switch, “M13,” is turned ON.

The power switching module 206-2 includes the latch circuit, “L2,”configured to have a definite state at power-up of the battery powersource and a logic circuit 210-2 configured to prevent cross conductionbetween the wireless power source 202-1 and the battery power source202-2 and to connect/disconnect the battery power source to/from theoutput terminal 212 of the power management circuit 204. In theembodiment depicted in FIG. 2, the latch circuit, “L2,” is a back toback inverter latch circuit that includes two inverters, “INVL21,”“INVL22,” which are connected back to back. The back to back inverterlatch circuit has a dynamic switching point threshold that scales wellwith the voltage level of the battery power source and allows the backto back inverter to have a defined state at power-up of the batterypower source with a good noise margin. In some embodiments, the latchcircuit is overridden by a driver circuit to flip the state based on apower-up preference setting. The logic circuit includes a cross-coupledcircuit 211-2, which includes four transistors, “M5,” “M6,” “M7,” “M8,”a power switch that is implemented as a PMOS transistor, “M14,” andtransistors, “M11,” “M12.” A node, “N3,” between the PMOS transistor,“M5,” and the NMOS transistor, “M6,” is connected to a terminal 226(e.g., a drain terminal or a source terminal) of the PMOS transistor,“M7.” A node, “N4,” between the PMOS transistor, “M7,” and the NMOStransistor, “M8,” is connected to a terminal 228 (e.g., a drain terminalor a source terminal) of the NMOS transistor, “M6.” Gate terminals 230,232 of the PMOS transistor, “M5,” and the NMOS transistor, “M6,” areconnected to a terminal, “c,” of the latch circuit, “L2.” Gate terminals234, 236 of the PMOS transistor, “M7,” and the NMOS transistor, “M8,”are connected to a terminal, “b,” of the latch circuit, “L1,” of thepower switching module 206-1. The cross-coupled circuit 211-2 allows abreak before a make operation to inhibit or prevent a current pathbetween the battery voltage, “V_(CC),” and the RF electromagneticvoltage, “V_(RF)” In an embodiment, the cross-coupled circuit 211-2ensures that the switch, “M13,” is switched off before the switch,“M14,” is turned ON.

In the embodiment depicted in FIG. 2, the latch circuits “L1,” “L2” ofthe power management circuit 204 have a definite state at power-up ofthe wireless power source 202-1 and the battery power source 202-2,respectively, which allows the power management circuit to work withvarious power-up sequences of the power sources. In an embodiment, thesizes of the inverters, “INVL11,” “INVL12,” “INVL21,” “INVL22,” arechosen such that terminal/node, “a,” terminal/node, “b,” is low andhigh, respectively, during a power-up of the wireless power source,while terminal/node, “c,” terminal/node, “d,” is low and high,respectively, during a power-up of the battery power source. A drivercircuit, such as a flip circuit, can override the state of the latchcircuits.

FIG. 3A depicts an embodiment of the latch circuit, “L1” or “L2,”depicted in FIG. 2. In the embodiment depicted in FIG. 3A, a latchcircuit 308 includes two inverters 336, 338 that are connectedback-to-back to form a latch configuration. The top inverter 336includes a PMOS transistor 340 and an NMOS transistor 342. The gateterminal 350 of the PMOS transistor 340 is connected to the drainterminal 352 of the NMOS transistor 342. The bottom inverter 338includes a PMOS transistor 344 and an NMOS transistor 346. The gateterminal 354 of the PMOS transistor 344 is connected to the drainterminal 356 of the NMOS transistor 346. In some embodiments, the sizesof the inverters are chosen such that the PMOS transistor in one of theinverters is much stronger than the NMOS in the inverter while thereverse is true for the other inverter. The DC characteristics of suchan arrangement allow the latch circuit 308 to go in a defined state atpower up. Specifically, the output of an inverter with the stronger PMOSgoes to a high state and the output of the inverter with the strongerNMOS transistor goes to a low state. FIG. 3B depicts a switching pointthreshold diagram of the latch circuit depicted in FIG. 3A. In oneembodiment, the aspect ratio (P/N) of the top inverter 336 is largerthan 4 and the aspect ratio (P/N) of the bottom inverter 338 is kept at0.25. In this embodiment, the switching point of the top inverter isaround 66% of the instantaneous supply voltage level and the switchingpoint of the bottom inverter is kept at around 33% of the instantaneoussupply voltage level. In one embodiment, the NMOS transistor is replacedby multiple NMOS transistors that are cascaded.

In an example of an operation of the latch circuit 308, outputs of bothinverters 336, 338 are at a low state initially. As power starts rampingup, the PMOS transistors 340, 344 of both inverters are ON, which causesboth inverter outputs to follow the power supply ramp up. The topinverter 336 starts to pull its output stronger than the bottom inverter338 at the same time the bottom inverter 338 starts pulling its outputlow stronger than the inverter 336. As the top inverter 336 startspulling its output high, the PMOS transistor of the bottom inverter 338gets weaker and the NMOS transistor of the bottom inverter 338 getsstronger. Similarly as the bottom inverter is pulling its output low,the PMOS transistor of the top inverter is driven strongly and the NMOStransistor of the top inverter gets weaker. Therefore, both theinverters aid each other to get to the same steady stable state. Bychoosing the sizes of the inverters 336, 338, a stable state of thelatch circuit can be achieved. In an embodiment, the sizes of theinverters 336, 338 are chosen such that the top inverter 336 pulls itsoutput high above “the high switching point threshold” of the bottominverter 338, driving its output to high while the bottom inverter 338pulls its output low below the “low switching point threshold” of thetop inverter 336, driving its output to low. In this embodiment, astable state in which the output of the bottom inverter 336 is set tohigh can be achieved. Sizing the inverters in such a manner can maintainthe noise margin of the circuit. For example, a dip or noise in thepower supply due to switching can be a common mode signal to the twoinverters 336, 338 and the switching point threshold of the invertersscale down with the power source, which provides good noise margin andallows a reliable steady state output for the latch circuit 308.

Turning to FIG. 2, the power management circuit 204 depicted in FIG. 2requires no particular power-up sequence of the power sources 202-1,202-2 to be followed. For example, the power management circuit can workwith a power-up sequence where the RF power source is present and thebattery power source is absent, a power-up sequence where the batterypower source is present and the RF power source is absent, a power-upsequence where the RF power source is present first and the batterypower source is present later, a power-up sequence where the batterypower source is present first and the RF power source is present later,and a power-up sequence where the battery power source and the RF powersource are present simultaneously. FIGS. 4-8 depict signal diagrams ofthe power management circuit under 5 different power-up sequences.

FIG. 4 depicts a signal diagram of the power management circuit depictedin FIG. 2 in a power-up sequence where the RF power source 202-1 comesup and the battery power source 202-2 is absent. As shown in FIG. 4, thewireless power source with a voltage, “V_(RF),” is applied to the powermanagement circuit 204 while the battery power source with a voltage,“V_(CC),” is turned OFF. When the voltage, “V_(RF),” of the wirelesspower source ramps up, the terminal/node, “a,” of the latch circuit,“L1,” is driven low and the terminal/node, “b,” of the latch circuit,“L1,” is driven high. The other latch circuit, “L2,” which is connectedto the voltage, “V_(CC),” drives both terminals/nodes, “c,” “d,” lowbecause the battery power source is absent. Because the signal at theterminal, “a,” is low, the gate of the V_(CC) switch (i.e., thetransistor, “M14,”) is driven to high, which switches off thetransistor, “M14.” The gate of the transistor, “M9,” is driven highthrough the transistors, “M1,” “M3,” which pulls down the gate of theV_(RF) switch (i.e., the transistor, “M13,”) and connects the wirelesspower source to the output of the power management circuit. During thepower-up sequence, the power management circuit depicted in FIG. 2ensures that the switch, “M14,” is switched off before the switch,“M13,” is turned ON, which prevents cross conduction between the powersources.

FIG. 5 depicts a signal diagram of the power management circuit 204depicted in FIG. 2 in a power-up sequence where the battery power sourcecomes up and the RF power source is absent. As shown in FIG. 5, thebattery power source 202-2 with a voltage, “V_(CC),” is applied to thepower management circuit while the wireless power source with a voltage,“V_(RF),” is turned OFF. When the voltage, “Vcc,” of the battery powersource ramps up, the terminal, “c,” of the latch circuit, “L2,” isdriven low and the terminal, “d,” of the latch circuit, “L2,” is drivenhigh. The other latch circuit, “L1,” which is connected to the wirelessvoltage, drives both terminals, “a,” and “b,” low because the wirelesspower source is absent. Because the terminal, “c,” of the latch circuit,“L2,” is low, the gate of the V_(RF) switch (i.e., the transistor,“M13,”) is driven to high, which switches off the transistor, “M13.” Thegate of the transistor, “M11,” is driven high through the transistors,“M5” and “M7,” which pulls down the gate of the V_(CC) switch (i.e., thetransistor, “M14,”) and connects the battery power source to the outputof the power management circuit. During the power-up sequence, the powermanagement circuit depicted in FIG. 2 ensures that the transistor,“M13,” is switched off before the transistor, “M14” is turned ON, whichprevents cross conduction between the power sources.

FIG. 6 depicts a signal diagram of the power management circuit 204depicted in FIG. 2 in a power-up sequence where the RF power source202-1 comes up first and the battery power source 202-2 comes up later.As shown in FIG. 6, the wireless power source with a voltage, “V_(RF),”is present first and the battery power source with a voltage, “V_(CC),”is present later. When the voltage V_(RF) of the wireless power sourceramps up, the terminal, “a,” of the latch circuit, “L1,” is driven lowand the terminal, “b,” of the latch circuit, “L1,” is driven high.Because the battery power source is absent, the terminals, “c,” and “d,”of the latch circuit, “L2,” both are driven low and the wireless powersource is connected to the output of the power management circuit. Theterminal/node, “e,” of the buffer circuit, “B1,” is also driven highafter a delay time of the buffer circuit, which switches ON the NMOStransistor, “M10,” connected between the gate terminal of the switch,“M13,” and ground.

When the battery power source 202-2 comes up, the terminal, “c,” of thelatch circuit, “L2,” is driven low while the terminal, “d,” of the latchcircuit, “L2,” is driven high. The V_(CC) switch (i.e., the transistor,“M14,”) is turned ON because the terminal, “c,” of the latch circuit,“L2,” is driven low. At the same time, because the terminal, “d,” of thelatch circuit, “L2,” is driven high, it attempts to switch OFF thetransistor, “M13.” However, due to the parallel transistor, “M10,”holding the gate of the transistor “M13” low, the V_(RF) switch (i.e.,the transistor, “M13,”) remains ON, causing no interruption in theoutput source. The switching ON of the V_(CC) switch (i.e., thetransistor, “M14,”) can be delayed if required by using a RC circuit ora logic signal derived from a voltage level detector to make sure thatthe voltage, “V_(CC),” of battery power source is high enough beforeconnection to avoid current going from the RF power source 202-1 to thebattery power source 202-2 and dip in output of the power managementcircuit 204.

Once the V_(CC) switch (i.e., the transistor, “M14,”) is turned ON, theAnd gate (A1) output driven by inputs at terminals, “x,” and “d,” goeshigh, which flips the default state of the latch, “L1,” connected to thewireless power source 202-1. In this case, the terminal, “a,” of thelatch circuit, “L1,” is driven high and the terminal, “b,” of the latchcircuit, “L1,” is driven low, which switches off the transistor, “M13,”and keeps the transistor, “M14,” ON, connecting the battery power source202-2 to the output. During the transition from the wireless powersource 202-1 to the battery power source 202-2, there is a short circuitpath between the battery power source and ground through thetransistors, “M5” and “M10.” The short circuit path is a momentaryphenomenon and the path is disconnected as soon as the And gate (A1)flips the state of the latch circuit, “L1,” and the terminal, “e,” ofthe latch circuit, “L1,” is driven low. To limit the current during thistransition, a high value resistor, “R1,” is used in the path between thepower switching modules 206-1, 206-2 of the power management circuit204. In an embodiment, the resistance of the resistor, “R1,” is chosensuch that the RC time constant to switch ON the switch, “M13,” fallswithin a predefined threshold.

FIG. 7 depicts a signal diagram of the power management circuit 204depicted in FIG. 2 in a power-up sequence where the battery power source202-2 comes up first and the RF power source 202-1 comes up later. Asshown in FIG. 7, the battery power source with a voltage, “V_(CC),” ispresent first and the wireless power source with a voltage, “V_(RF),” ispresent later. When the voltage, “Vcc,” of the battery power sourceramps up, the terminal, “c,” of the latch circuit, “L2,” is driven lowand the terminal, “d,” of the latch circuit, “L2,” is driven high, whilethe terminals, “a,” and “b,” of the latch circuit, “L1,” both are drivenlow, which turns ON the transistor, “M14.” Both the input terminals,“x,” and “d,” of the And gate, “A1,” are driven high. However, becausethe wireless power source is not present, the output of the And gate,“A1,” is still low. When the wireless power source comes up, the Andgate, “A1,” output is driven high. The high state at the outputterminal, “a,” of the And gate, “A1,” flips the default state of thelatch, “L1,” to keep the V_(CC) switch (i.e., the transistor, “M14,”) ONand the V_(RF) switch (i.e., the transistor, “M13,”) remains in an OFFcondition, causing the required power source (in this case the battery)to be connected to the output terminal 212 of the power managementcircuit 204.

FIG. 8 depicts a signal diagram of the power management circuit 204depicted in FIG. 2 in a power-up sequence where the battery power source202-2 and the RF power source 202-1 come up simultaneously. As shown inFIG. 8, the battery power source with a voltage, “V_(CC),” and thewireless power source with a voltage, “V_(RF),” are present at the sametime. When both the battery power source and the wireless power sourceramps up at the same time, the terminals, “a,” and, “c,” of the latchcircuits, “L1,” “L2,” are driven low, the terminals, “b,” and “d,” ofthe latch circuits, “L1,” “L2,” are driven high. Gates of both theswitches, “M13,” and “M14,” are driven high and the switches, “M13,” and“M14,” are switched OFF. Once both the input terminals, “x,” and “d,” ofthe And gate, “A1,” are driven high, the And gate, “A1,” flips the stateof the latch, “L1,” which turns the gate of the transistor, “M11,” high.The high state of the transistor, “M11,” pulls down the gate of thetransistor, “M14,” which turns ON the transistor, “M14,” and connectingthe battery power source to the output of the power management circuit.The V_(RF) switch (i.e., the transistor, “M13,”) remains OFF. Althoughthe signal at the terminal, “e,” goes up initially after the terminal,“b,” of the latch circuit, “L1,” is driven high, the gate of thetransistor, “M10,” is driven low because the output source is still notramped up and the output of And gate, “A2,” remains low. As shown in thewaveform, both switches, “M13,” and “M14,” are OFF initially, and thenthe battery power source is applied to the output of the powermanagement circuit 204, while the V_(RF) switch (i.e., the transistor,“M13,”) remains in switched OFF condition. In one embodiment, the thepower management circuit 204 is implemented in an electronic device thatis connected to AC power and the battery power source 202-2 is achargeable battery that is charged by the mains voltage via a rectifierand charger circuit.

FIG. 9 depicts a second embodiment of the power management circuit 104depicted in FIG. 1 that is used with a wireless power source 902-1 and abattery power source 902-2. The wireless power source 902-1 and thebattery power source 902-2 may be similar to or the same as the wirelesspower source 202-1 and the battery power source 202-2. The differencebetween the power management circuit 904 depicted in FIG. 9 and thepower management circuit 204 depicted in FIG. 2 is that the powermanagement circuit 904 depicted in FIG. 9 does not include transistors,“M2,” “M6.” In the embodiment depicted in FIG. 2, the transistors, “M2,”“M6,” are retained for symmetry and balance of load for the latchcircuits, “L1,” “L2.” In the embodiment depicted in FIG. 9, the powermanagement circuit 904 includes two power switching modules 906-1,906-2. The power switching module 906-1 includes the latch circuit,“L1,” configured to have a definite state at power-up of the wirelesspower source and a logic circuit 910-1 configured to prevent crossconduction between the wireless power source and the battery powersource and to connect/disconnect the wireless power source to/from anoutput terminal 912 of the power management circuit 204. The logiccircuit 910-1 includes a cross-coupled circuit 911-1, which includesthree transistors, “M1,” “M3,” “M4,” a power switch that is implementedas a PMOS transistor, “M13,” AND gates, “A1,” “A2,” a buffer circuit,“B1,” transistors, “M9,” “M10,” and a resistor, “R1.” A terminal 914(e.g., a drain terminal or a source terminal) of the PMOS transistor,“M1,” is connected to a terminal 916 (e.g., a drain terminal or a sourceterminal) of the PMOS transistor, “M3.” A gate terminal 918 of the PMOStransistor, “M1,” is connected to a terminal, “a,” of the latch circuit,“L1.” Gate terminals 920, 922 of the PMOS transistor, “M3,” and the NMOStransistor, “M4,” are connected to the latch circuit, “L2,” of the powerswitching module 906-2. The power switching module 906-2 includes thelatch circuit, “L2,” configured to have a definite state at power-up ofthe battery power source and a logic circuit 910-2 configured to preventcross conduction between the wireless power source and the battery powersource and to connect/disconnect the battery power source to/from theoutput terminal 912 of the power management circuit 204. The logiccircuit 910-2 includes a cross-coupled circuit 911-2, which includesthree transistors, “M5,” “M7,” “M8,” a power switch that is implementedas a PMOS transistor, “M14,” and transistors, “M11,” “M12.” A terminal924 (e.g., a drain terminal or a source terminal) of the PMOStransistor, “M5,” is connected to a terminal 926 (e.g., a drain terminalor a source terminal) of the PMOS transistor, “M7.” A gate terminal 928of the PMOS transistor, “M5,” is connected to a terminal, “c,” of thelatch circuit, “L2.” Gate terminals 930, 932 of the PMOS transistor,“M7,” and the NMOS transistor, “M8,” are connected to the terminal, “b,”of the latch circuit, “L1,” of the power switching module 906-1. Theoperation of the power management circuit 904 may be similar to or thesame as the operation of the power management circuit 204.

FIG. 10 is a process flow diagram of a method for operating a powermanagement circuit in accordance with an embodiment of the invention.The power management circuit may be similar to or the same as the powermanagement circuit 104 depicted in FIG. 1, the power management circuit204 depicted in FIG. 2, and/or the power management circuit 904 depictedin FIG. 9. At block 1002, power switching modules are provided, wherepower is supplied to each of the power switching modules by at least oneof multiple power sources. At block 1004, a latch circuit of each of thepower switching modules is operated to have a definite state at power-upof a corresponding power source. At block 1006, cross conduction betweenthe power sources is prevented using a logic circuit of each of thepower switching modules. At block 1008, one of the power sources isconnected to an output of the power management circuit based on thedefinite states of the latch circuits.

Although the operations of the method herein are shown and described ina particular order, the order of the operations of the method may bealtered so that certain operations may be performed in an inverse orderor so that certain operations may be performed, at least in part,concurrently with other operations. In another embodiment, instructionsor sub-operations of distinct operations may be implemented in anintermittent and/or alternating manner.

In addition, although specific embodiments of the invention that havebeen described or depicted include several components described ordepicted herein, other embodiments of the invention may include fewer ormore components to implement less or more feature.

Furthermore, although specific embodiments of the invention have beendescribed and depicted, the invention is not to be limited to thespecific forms or arrangements of parts so described and depicted. Thescope of the invention is to be defined by the claims appended heretoand their equivalents.

What is claimed is:
 1. A power management circuit comprising: aplurality of power switching modules, wherein power is supplied to eachof the power switching modules by at least one of a plurality of powersources, wherein each of the power switching modules comprises: a latchcircuit configured to have a definite state at power-up of acorresponding power source; and a logic circuit configured to controlpower supplied from the corresponding power source in response to thedefinite state of the latch circuit, wherein the logic circuit comprisesa cross-coupled circuit.
 2. The power management circuit of claim 1,wherein the latch circuit of each of the power switching modulescomprises a back-to-back inverter latch circuit, and wherein theback-to-back inverter latch circuit comprises two inverters that areconnected back-to-back.
 3. The power management circuit of claim 2,wherein each inverter comprises a PMOS transistor and an NMOStransistor, and wherein a gate terminal of the PMOS transistor isconnected to a drain terminal of the NMOS transistor.
 4. The powermanagement circuit of claim 1, wherein the logic circuit is configuredto prevent cross conduction between the power sources.
 5. The powermanagement circuit of claim 4, wherein the cross-coupled circuitcomprises a first PMOS transistor, a first NMOS transistor, a secondPMOS transistor, and a second NMOS transistor, wherein a node betweenthe first PMOS transistor and the first NMOS transistor is connected toa drain terminal or a source terminal of the second PMOS transistor, andwherein a node between the second PMOS transistor and the second NMOStransistor is connected to a drain terminal or a source terminal of thefirst NMOS transistor.
 6. The power management circuit of claim 5,wherein within each of the power switching modules, gate terminals ofthe first PMOS transistor and the first NMOS transistor are connected toa terminal of the latch circuit, and wherein gate terminals of thesecond PMOS transistor and the second NMOS transistor are connected to alatch circuit of another power switching module.
 7. The power managementcircuit of claim 4, wherein the cross-coupled circuit comprises a firstPMOS transistor, a second PMOS transistor, and an NMOS transistor, andwherein a source terminal or a drain terminal of the first PMOStransistor is connected to a drain terminal or a source terminal of thesecond PMOS transistor.
 8. The power management circuit of claim 7,wherein within each of the power switching modules, a gate terminal ofthe first PMOS transistor is connected to a terminal of the latchcircuit, and wherein gate terminals of the second PMOS transistor andthe NMOS transistor are connected to a latch circuit of another powerswitching module.
 9. The power management circuit of claim 4, whereinthe logic circuit further comprises a switch circuit connected to thecorresponding power source.
 10. The power management circuit of claim 1,wherein the logic circuit is configured to connect the correspondingpower source to an output terminal of the power management circuit or todisconnect the corresponding power source from the output terminal ofthe power management circuit.
 11. The power management circuit of claim1, wherein the plurality of power sources comprises a battery powersource or a wireless power source.
 12. The power management circuit ofclaim 1, wherein the plurality of power sources comprises a wirelesspower source and a battery power source.
 13. An integrated circuit (IC)comprising: the power management circuit of claim 1; and a battery powersource.
 14. A power management circuit comprising: a first powerswitching module, wherein power is supplied to the first power switchingmodule by a wireless power source; a second power switching module,wherein power is supplied to the second power switching module by abattery power source, wherein each of the first and second powerswitching modules comprises: a back-to-back inverter latch circuitconfigured to have a definite state at power-up of a corresponding powersource; and a logic circuit configured to control power supplied fromthe corresponding power source in response to the definite state of theback-to-back inverter latch circuit, wherein the logic circuitcomprises: a cross-coupled circuit; and a switch circuit connected tothe corresponding power source.
 15. The power management circuit ofclaim 14, wherein the back-to-back inverter latch circuit of each of thefirst and second power switching modules comprises two inverters thatare connected back-to-back, wherein each inverter comprises a PMOStransistor and an NMOS transistor, and wherein a gate terminal of thePMOS transistor is connected to a drain terminal of the NMOS transistor.16. The power management circuit of claim 15, wherein the logic circuitis configured to prevent cross conduction between the wireless powersource and the battery power source.
 17. The power management circuit ofclaim 16, wherein the cross-coupled circuit comprises a first PMOStransistor, a first NMOS transistor, a second PMOS transistor, and asecond NMOS transistor, wherein a node between the first PMOS transistorand the first NMOS transistor is connected to a drain terminal or asource terminal of the second PMOS transistor, wherein a node betweenthe second PMOS transistor and the second NMOS transistor is connectedto a drain terminal or a source terminal of the first NMOS transistor,wherein within each of the first and second power switching modules,gate terminals of the first PMOS transistor and the first NMOStransistor are connected to a terminal of the latch circuit, and whereingate terminals of the second PMOS transistor and the second NMOStransistor are connected to a latch circuit of another power switchingmodule.
 18. The power management circuit of claim 16, wherein thecross-coupled circuit comprises a first PMOS transistor, a second PMOStransistor, and an NMOS transistor, wherein a source terminal or a drainterminal of the first PMOS transistor is connected to a drain terminalor a source terminal of the second PMOS transistor, wherein within eachof the first and second power switching modules, a gate terminal of thefirst PMOS transistor is connected to a terminal of the latch circuit,and wherein gate terminals of the second PMOS transistor and the NMOStransistor are connected to a latch circuit of another power switchingmodule.
 19. An integrated circuit (IC) comprising: the power managementcircuit of claim 14; and the battery power source.
 20. A method foroperating a power management circuit, the method comprising: providing aplurality of power switching modules, wherein power is supplied to eachof the power switching modules by at least one of a plurality of powersources; operating a latch circuit of each of the power switchingmodules to have a definite state at power-up of a corresponding powersource; preventing cross conduction between the power sources using alogic circuit of each of the power switching modules; and connecting oneof the plurality of power sources to an output of the power managementcircuit based on the definite states of the latch circuits.